Backwards compatibility: When can (and should) vendors cry uncle?

My ZDNet blogging colleague David Berlind is sounding the bell --- actually, more like calling in a five-alarmer -- regarding the fact that older versions of Intuit's QuickBooks won't work on Windows Vista.

I love a conspiracy blaze as much as the next blogger. But I'm not sure I am seeing as much smoke and fire as Berlind on this one.

I chatted with Intuit QuickBooks Product Manager George Jacquette this week about Intuit's Vista plans. Jacquette said that QuickBooks 2007, which the company rolled out last fall, is Intuit's solution for customers who want to run the company's accounting suite on Microsoft's latest Windows release. Intuit is releasing some downloadable patches for things like 64-bit Vista support in order to make sure that QuickBooks 2007 works right on Vista, starting on January 30, when Vista becomes available worldwide.

What about earlier versions of QuickBooks?

"We are not going to support (Vista) with our earlier versions," Jacquette said. "Microsoft changed file management and permissions in Vista in a way that it won't make it easy for our core QuickBooks product to be easily rewritten to support."

Is Intuit mad that Vista "broke" older versions of QuickBooks? Jacquette didn't seem overly concerned.

"Security enhancements like standard user in Vista are needed. In the past, you needed to be an administrator to be a QuickBooks user. Now, you don't have to. This change is for the global good," he said.

A more pertinent question, of course, is whether QuickBooks users will scream bloody murder over the fact they can't use older copies of QuickBooks on Vista. Berlind found one user who is none too happy. But will others care?

Accounting software isn't something that will make use of the fancy Aero graphics that are part of Vista. And like lawyers, accountants don't strike me as folks who strive to be on the cutting edge of technology.

Another question: Is it Intuit's fault that its older products don't work on Vista? Or Microsoft's fault for changing the operating system in a way that it breaks them? The fact that Microsoft has decided not to make available publicly a list of apps that don't work right with Vista makes me wonder whether there could be lots more examples like QuickBooks. But when an application vendor throws in the towel and decides agains trying to retrofit apps, can and should Microsoft be blamed?

To me, Intuit is making the choice Apple made a few years back when it drew a line in the sand and decided to cut off bakcwards compatibility for users of older versions of the Mac OS operating system. Microsoft has yet to do the same, although a number of company watchers believe that it won't take the Redmondians too much longer to decide that it can't keep make supporting old versions of third-party and Microsoft apps a priority.

What do you think? When can -- and should -- Microsoft decide to release a less bloated, less-dependency-ridden version of Windows, even if it breaks older apps? What should be the cut-off point for backwards compatibility support? Apps up to five years old will be guaranteed to work? Ten?

And any mad QuickBooks customers out there who are champing at the bit to run older versions of your software on Vista? If you're out there, weigh in.